Basal rates from a pump replace the long-acting insulin doses taken by those on injections. This provides an around-the-clock delivery of insulin that stops the liver from making and releasing excess glucose into the bloodstream. Most pumps can change basal delivery every 1 to 30 minutes in increments as small as 0.01 to 0.025 units per hour.
Accurate basal rates keep glucose readings level overnight or when meals are skipped during the day. When someone has their basal rates set correctly, their glucose will rise or fall no more than 30 mg/dL (1.7 mmol) during 8 hours of sleep or during any 5-hour period of fasting while they are awake.
Basal rates usually make up about 50% of the total daily dose (TDD) of insulin.11,12 Effective basal rates rarely fall below 40% and occasionally rise above 60% of the TDD. Carb boluses make up most of the remainder, with a small percentage of the TDD, usually less than 9%, used for correction boluses.
Many teens and adults require a higher basal rate in the predawn hours to counteract a natural increase in growth hormone production that starts at about 3 am each day. This normal rise in glucose production is called the dawn phenomenon. If no extra insulin is provided, the glucose will rise and be high when the person wakes up. As a person approaches middle age, the dawn phenomenon often declines or disappears entirely.
To accommodate changes in basal need, pumps provide temporary basal rates that can be increased or decreased in 1% to 10% increments for 1 to 72 hours as needed for illness, exercise, or other situations. Temporary rates can be increased to handle occasional illnesses or decreased during and after long periods of exercise or activity.
Most pumps also allow for alternate basal profiles to be entered into a pump. Someone wearing a pump can also switch between alternate basal profiles if their insulin needs differ on weekends versus weekdays, or on several days a month during menses for women. Alternate basal profiles can be especially helpful for people whose activities vary from day to day.
Alternate basal profiles currently adjust only basal rates, not the CarbF and CorrF that accompanies the basal profile. Future pumps may allow carb and correction factors to be adjusted in tandem with the basal profile.